The present invention is directed to an improved electrode assembly and to a system and method for welding projection weld nuts to a work piece therewith.
Projection weld nuts are well known to those of skill in the art. In brief, projection weld nuts are generally threaded nuts designed especially for attachment to a metallic work piece via resistance welding. To facilitate welded attachment, projection weld nuts include several portions of weld material that project outward from a welding face (i.e., the face of the projection weld nut that will contact the work piece). The projection weld nut is placed into contact with a work piece, typically in or over a pilot hole, pressure is preferably applied, and a resistance welding apparatus is used to pass current through the work piece and the projection weld nut. The current causes a melting of the weld material projections and a welding of the projection weld nut to the work piece.
In a typical projection weld nut welding process, a projection weld nut is located to a work piece for welding. The work piece is often maintained in the welding position by hand. Welding is typically accomplished by use of a specialized fixed position resistance welding device that includes a pair of electrodes designed to apply pressure to the projection weld nut and work piece and to pass current through the work piece and the projection weld nut. For example, a first electrode may be provided to contact a top surface of the work piece while a second electrode is provided to contact the projection weld nut, which is maintained in contact with the underside of the work piece. Each of the electrodes is normally pressed against the work piece by an actuator, such as a hydraulic or pneumatic cylinder.
The problem with such a system is that it requires specialized equipment (e.g., a stationary pedestal welder) unique to the work piece at issue, and also commonly necessitates much handling by an operator. In contrast, the present invention allows projection weld nuts to be attached to a work piece using a weld gun, such as a servo weld gun. This would then permit the use of a welding robot or other manipulator, which can be easily adapted for use with work pieces of varying size and/or shape so as to eliminate the need for a specialized resistance welding apparatus and minimize operator handling of work pieces to which weld nuts will be attached.
The system and method of the present invention further eliminates other problems commonly associated with the welding of projection weld nuts. For example, a system and method of the present invention automatically compensates for weld tip wear and permits a positional adjustment of a sheet metal work piece in up to three directions without causing any welding problems.